Security systems are becoming widespread in use with most commercial establishments and many residential establishments having security systems installed. Such security systems generally include a control panel which controls the overall operation of the system, one or more keypad controllers for user access to the system and various detectors and sensors. The control panel is generally mounted in an area of restricted access, such as a utility room or basement, and contains the system electronics, back-up power sources, and includes an interface for remote monitoring and two way communication over telephone lines or other systems. Security systems are generally divided into several zones or areas of protection and each of these zones generally has one or more detection devices or sensors such as motion detectors, door or window contacts, glass break detectors, or shock sensors connected to it. In some security systems, smoke detectors or other fire detection devices may also be connected to the control panel.
Security systems generally have one or more means for a user to access the system, such as, keypad controllers which are used by the user to instruct the security system. The keypad controller is used to send commands to the system to control the operation of the system and may also display system information. Such keypad controllers generally have a status display which may include either individual indicators, such as light emitting diodes or may include a LCD or LED display, which is capable of displaying a number of alpha-numeric characters used to display simple messages regarding the status and operation of the system. Recently, graphical controllers have also been proposed having a graphical display screen capable of displaying a floor plan of the premises at which the security system is installed.
The keypad controller is also used by the user to arm and disarm the security system. Each user of a security system is given a unique personal identification number or PIN, which is generally a sequence of numbers which are entered by the user, in order, on the numeric keypad. When arming the system, the user enters their PIN at which time the system will be armed and will generally provide a delay time to enable the user to exit the premises at which the system is located before the system becomes fully armed. Upon entering a premise having an armed security system, the user would enter their PIN at which time the security system would be disarmed. During disarming of the security system, there is generally a delay time to enable the user to enter their PIN before the system will go into alarm mode.
The security system is generally set up to permit a number of attempts of entry of the PIN by a user. This is so that, should a user incorrectly enter their PIN, they will be given another opportunity to enter the PIN correctly. This situation may arise where the user has either pressed a wrong number key in the sequence of their PIN, has entered a number in the sequence twice, or has inadvertently skipped entering a number in the sequence. While a number of security systems give an audible feedback by sounding a tone with each key-press, in some situations, the user may not be able to hear the tone clearly, and thus, may enter the PIN incorrectly. At the present time, a number of such security systems examine the number sequence of the PIN in a block. Thus, for example, if the PIN is a sequence of four numbers, the security system will examine the first four numbers entered to determine whether a match exists against the authorized access codes programmed in its memory. If no match is found, then the security system will wait for the next four numbers to be entered and repeat the matching of those numbers. A number of security systems also provide the capability of clearing the numbers entered if the user has realized they have made a mistake during the entry of the number sequence. Thus, the user may clear the numbers and start again at the beginning. In order to maintain the integrity of the security system, the security systems are generally programmed to allow a limited number of attempts for the PIN entry before the security system will lock-out the keypad and not permit any further attempts.
While the above types of security systems do provide for some flexibility in the event that a user incorrectly enters their PIN, there are some circumstances in which the user may be continually entering the wrong PIN and would not be aware of that situation. This circumstance could arise if the user has double entered a number or has skipped a number. In these circumstances, the block of numbers being examined by the security system for a valid access code would be shifted and even if the user were entering the correct PIN on the second or third attempt, because of this shift of the number key examination, no valid match with a PIN would be identified. There thus, remains a need for a security system which will overcome these difficulties.